Isolation substrate ring for plasma reactor

ABSTRACT

A radio frequency (RF) glow discharge plasma etch electrode design is disclosed which is capable of creating high power density plasma with uniform etch rates, while providing access for automatic loading semiconductor wafers from outside of the plasma region. The electrode assembly comprises of an electrode to which RF energy is applied surrounded by an insulator, which in turn surrounded a grounded surface all of which have cylindrical symmetry. When placed a small distance from a flat, grounded substrate, the electrode assembly creates a volume which can effectively combine a high power density plasma, while maintaining a sufficient channel for pumping a gas flow and for observing the plasma optically. The same channel is widened for automatic transport of semiconductor wafers from outside of the plasma reactor chamber. Such confined high power density plasma are important for high rate, uniform, anisotropic etching, especially for silicon dioxide.

This is a divisional of application Ser. No. 663,805 filed Oct. 22,1984, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a semiconductor manufacturing apparatus and inparticular to a semiconductor manufacturing apparatus in which circuitpatterns are etched on a semiconductor wafer by a plasma reaction.

This invention relates to commonly assigned U.S. Pat. Nos. 4,657,671;4,654,106; 4,659,413; 4,695,700; 4,657,618; 4,657,620; 4,657,621; and4,661,196 and U.S. application Ser. Nos. 663,904 now abandoned, 663,805now abandoned, and 663,906 now abandoned, which by reference areincorporated herein.

The manufacturing of semiconductor devices such as a 256K RAM or even upto a 1 megabit RAM device require precision dry etching with highrepeatability, low particulate levels, reliable endpoint detection,multiple process capability and reliable feedback control to amicroprocessor controller for reliable systems execution. An example ofa prior art plasma reactor system is described in U.S. Pat. No.3,757,733 which is assigned to the assignee of the present invention.

In the prior art systems, the transportation of silicon wafers through aplasma reactor required an opening in the reactant chamber that is largeenough for the wafer to pass through. The mechanism that are typicallyused create particles that potentially impact yeild of devices of thesemiconductor wafers that are processed.

Chlorine and bromine gases which are typically used in the processduring plasma etching are highly corrosive to the components that areused to build the plasma reactors. Over a long term operation, reactorcomponents exposed to the plasma must be constructed of materials thatare resistance to the corrosive effects of the plasma. Aluminum is anexcellent material of construction for a plasma reactor, especially whenit is protected by anodization. However, during etching, when asemiconductor or silicon wafer is placed on a substrate assembly that isanodized and used as an electrode, the substrate is protected from theplasma by the silicon wafer. However, each silicon wafer has a slice orflat to allow for crystallographic orientation. If the slice is placedon the substrate with random orientation of the flat, an annulus ofequal width of the flat width plus the placement tolerance will ingeneral be exposed to the plasma. Anodizing the whole substrate isimpractical in that it is conductive towards the RF electrical powerused in the plasma reactor. However, it is an insulator towards DC. Itis known that electrically floating objects such as silicon waferscovered with oxides exposed to a plasma will acquire an electricalpotential, the floating potential, above the ground of the system. Ithas been observed in production that an electrostatic repulsion developsbetween the wafer and the semiconductor substrate causing the wafer torandomly drift off its alignment position on the substrate.

Although several commercially available automatic wafer etch reactorsuse a confined plasma, none of the known systems provide a small gapwhich will not support a plasma and therefore confine the plasma withinthe small gap, use the same gap for both pumping the exhaust of gasesfrom the reactors and for transporting the semiconductor wafers into thereactant chamber and thus keeping the reactant chamber simple and freeor poorly controlled dead space within the reactor chamber.

Additionally, it has been determined that the gap between the collimatoror electrode and substrate during process should be approximately around0.040 inch for oxide processing. With a non-load locked system, theprocess chamber is vented to atmosphere which allows the electrode andcollimater to move up to between 0.030 and 0.040 inch and thesemiconductor wafer passes under the collimater. This is unreliable dueto the fact than an inconsistent gap can now be achieved and the slicelevitation varies, also, an automatic transportation system isimpractical with the above operation. And in particular, the singleslice dioxide and oxide etch processes have historically used thehighest possible density to remove silicon dioxide. This elevated powerdensity is far more difficult to control than any other type of etchingoperation. Also, highly selective etch processing often builds updeposits in the reactors. For this reason, these processes have tendedto be limited in commercial applications.

SUMMARY OF THE INVENTION

A plasma etch system that processes one slice at a time is disclosed.The system is comprised of an entry loadlock, an exit loadlock, a mainchamber, vacuum pumps, RF power supply, RF matching network, a heatexchanger, throttle valve and pressure control gas flow distribution anda microprocessor controller. A multiple slice cassette full of slices ishoused in the entry load lock and after pumping to process pressure, asingle slice at a time is moved by an articulated arm from the cassettethrough an isolation gate to the main process chamber. The slice isetched and removed from the main process chamber through a secondisolation gate by a second articulated arm to a cassette in the exitloadlock. The process is repeated until all semiconductor wafers havebeen etched. The cassette loadlock system is able to evacuate a wholecassete of semiconductor wafers for processing which lowers theparticulate environment for the slices and, provides a more stableenvironment for the slices by removal of moisture and preventing staticdischarges and additionally provides a safety feature that protects theoperators from harsh or toxic gases that are traditionally used insemiconductor type plasma reactors.

This novel feature enables clean slice handling and eliminates theproblem that traditionally occurs in the manufacturing of semiconductordevices in that there are no airtracks on the devices, no rubbing of theparts of semiconductor wafers. The semiconductor wafers are lifted offthe cassette slot before movement and all belts, pulleys or drives areeither external to the chamber or shielded within the main reactorchambers. The movement of the slices through the process is tracked withsensors.

The cassette loadlock apparatus according to the invention is a closedloop feedback process control system which insures that adequatepressure within the entry loadlock, the exit loadlock and the mainchamber are controlled by microprocessor. The RF power during thereaction of the manufacturing process is monitored and controlled by amicroprocessors. Gas flows are monitored and controlled by themicroprocessor through mass flow controllers. End of etch is monitoredand controlled by the microprocessor through a novel endpoint detectionscheme.

The invention provides a multiple process capability by which multiplemenus can be applied to a single slice in situ to achieve special etchprofiles and other special processing requirements such as highselectivity of the etch films to the substrate and the etching ofmultiple stacked films.

These features provide a high etch rate with high resist survivalthrough the use of a refrigerated liquid cooling on the top and bottomelectrodes, thus allowing high power with good photoresist preservationduring the operation.

These and other advantages and features of the invention will be moreapparent from reading of the specification in conjunction with thefigures in which:

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a front elevation of a cassette load lock plasma reactoraccording to the invention;

FIG. 2 is top view of the cassette load lock plasma reactor according tothe invention;

FIG. 3 is a block diagram of the control system for the plasma reactoraccording to the invention;

FIG. 4 is a block diagram for the RF circuit;

FIG. 5 is a block diagram for the endpoint detection logic;

FIG. 6 is a flow diagram of the endpoint detection process;

FIG. 7 are waveforms illustrating the detection of an endpoint;

FIGS. 8 and 9 are the gas and vacuum flow diagrams;

FIGS. 10 and 11 are different views of the cassette load lock plasmareactor;

FIGS. 12 through 13 illustrate the wafer transport system;

FIGS. 14 through 17 are drawings illustrating the slice transport arm;

FIG. 18 is a view of the entrance port of the plasma reactor;

FIGS. 19 and 20 are views illustrating the operation of the gate valves;

FIG. 21 is a sectional view of the reactor chamber;

FIG. 23 is a top vie of the plasma plate illustrating an anodized ring;

FIGS. 23 and 24 illustrate the electrical assembly;

FIG. 25 is a cross sectional view of an alternate embodiment of thereaction chamber;

FIGS. 26 through 28 are illustrations of the power load lock reactor;

FIGS. 29 and 30 are illustrations of the power load lock slice handlerarm; and

FIGS. 31 through 34 are diagrams of the powered load lock chambers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 there is shown a front elevation of a cassette load lockplasma reactor. The cassette of semiconductor wafers having photoresistpatterns printed on them is placed in an entry load lock 21. A processis entered into a microprocessor that is contained within the cassetteload lock reactor 23 by a keyboard 25 and a display 27. The menu isloaded in memory of the microprocessor and the process sequence begins.The entry load lock 21 is pumped down to a predetermined pressure orprocess pressure by a vacuum pump 29. The process pressure is maintainedby feedback control circuit via a manometer that provides information tothe microprocessor within the cassette load lock reactor 23 to control athrottle valve that is used to control the pump rate of the entry loadlock 21. At the time that the entry load lock 21 is being pumped down toa process pressure and maintained there, the main chamber is eitherpumped down to main process pressure or is maintained at processpressure by a main chamber pump 31. A cassette elevator that iscontained within the entry load lock 21 positions a first semiconductorwafer or slice that is to be processed by the cassette load lock reactor23 and in the embodiment shown in FIG. 1, a cassette that is a handlingdevice that stores a plurality or in the case of FIG. 1, 25semiconductor wafers. Each wafer has patterns for semiconductor circuitsprinted on them by a photoresist process. The first semiconductor waferis, as shown in FIG. 2, positioned by the cassette elevators locatedgenerally at 33. The semiconductor wafer is moved from the entry chamber21 through an isolation gate valve 35 into a main process chamber 37 andplaced on the main chamber bottom electrode 39 for etching by anarticulating arm 41. The position of the semiconductor wafer 143 iscontrolled by a feedback system and capacitive sensors that monitor themovement of the semiconductor wafer from the load lock chamber into themain chamber. After the slice is sensed to be safe in the main chamber37 and the articulating arm 41 is sensed to be moved back into the entryload lock 21, the isolation gate 35 is closed and appropriate gases areapplied from the gas distribution system 43 of FIG. 1 through thefiltering systems generally at 45 and applied to the main chamber 37 byflow controllers 845 that are contained within each gas line 45. In theembodiment of FIG. 1, up to four gases may be applied to the mainchamber for the process. Additionally, in FIG. 1, a nitrogen line 47provides nitrogen gas for purging of the system when it is necessary toopen up the main chamber, the entry load lock or the exit load lock 49.

As prescribed by the menu that was entered on the keyboard 25, pressureestablished by a throttle valve that is connected to the main chambervacuum pump 31 and a manometer pressure sensor and the feedback loopprocess control is maintained by the microprocessor within the cassetteload lock reactor 23. The cassette load lock reactor 23, in theembodiment of FIG. 1, is a plasma reactor and a plasma is formed byapplying RF energy between the two electrodes that are contained withinthe main chamber 37 which ionizes the gases to form reactant gases thatinclude ions, free electrons and molecular fragments. The gases areprovided by the gas distribution 43 and the filters 45. RF power isprovided to the main chamber 37 by an RF generator 51 and is applied toan RF matching network 53 by a conductor 55. The RF matching networkcontrols and adjusts the energy that is applied between the electrodesthat are contained within the main chamber by sensing the reflectedpower and converting this information to the digital signal that themicroprocessor within the cassette load lock 23 will respond to.

In either etching or deposition process, the processing is automaticallyterminated by the microprocessor within the cassette load lock reactor23. When in the etching mode, an endpoint is detected by an endpointdetector in the cassette load lock 23 which measures change in theoptical emissions at a specific wavelength. The cassette load lockreactor 23 that is shown in FIGS. 1 and 2 provide multiple menus to berun on the same slice by the proper selection during the menu entry tothe keyboard 25. After the process is complete, the slices orsemiconductor wafers are automatically removed from the main chamber bya second articulated arm 57 that is located within the exit load lock 49and is passed through a second isolation gate 61 and placed in an emptycassette whose position is positioned by the elevators at 63. At thecompletion of the processing of each semiconductor wafer, the process isrepeated until all of the semiconductor wafers have been processed bythe cassette load lock reactor after which the entry load lock 21 andthe exit load lock 49 are brought up to atmospheric pressure by applyingnitrogen through line 47 to purge the entry 21 or the exit load lock 49.The cassette is then removed and a new cassette is loaded forprocessing. Heat transfer from the slice during etching is accomplishedthrough a refrigerated system that is contained within a refrigeratorcontroller 63 that refrigerates in the embodiment of FIG. 1, an ethyleneglycol--water mixture flowing through the top and bottom electrodes thatare contained within the main chamber 37. A thermocouple sensor elementis used to monitor the temperature so that the process may be controlledby the microprocessor that is contained within the cassette load lockreactor 23. Additionally, the oil that is used by the main chambervacuum pump is re-circulated and filtered by a filter system 65.

FIG. 3 is a block diagram of a microprocessor control system 10 that isused to control the operation of the cassette load lock reactor 23. Inparticular, a central processing unit 17, which in the embodiment ofFIG. 1 is manufactured with a 9900 microprocessor that is manufacturedby Texas Instruments Incorporated of Dallas, Tex. or can be any centralprocessing unit known in the art that has similar specifications as tospeed, word length and operation.

The central processing unit 17 has an EPROM and RAM memory 19 whichstores data and program instructions that are used to control the I/Odevices that are connected to data bus 6. A language translator 15 isprovided which is used to convert SECS II protocall into internalprotocall that the CPU 17 will recognize. SECS II is an industrystandardized interface for semiconductor equipment communication. Thecentral processing unit or CPU 17 is connected to a data bus 6, whichinterfaces to the I/O devices. In particular, a battery memory RAM 13stores menu data that is provided to the processor system 10 of FIG. 3by the keyboard 25 and the display terminal 27. A digital I/O 3 providesdigital controls to control the process to include the gate valves andother controllable devices that are contained within the cassette loadlock reactor 23 or the power load lock reactor 523 of FIG. 26 andreceives status from these devices indicating the initiation ofoperation or the completion of operation. The status and control signalsthat are used to control the operation of the devices of FIG. 1 or arelisted in Table 1.

TABLE I Inputs (Status) and Outputs (controls) of the Digital I/O.

Device Status Controls

Gate valve 35 opened/closed open/close

Gate valve 61 opened/closed open/close

Valves 704 opened/closed open/close

Valves 705 open/closed

Valves 706 opened/closed open/closed

Valves 707 open/closed

Valves 708 opened/closed open/closed

Valves 709 open/closed

Valves 771 open/closed

Valves 773 open/closed

Valves 774 open/closed Purge on/off

Chamber gass on/off

RF on/off on/off

Gas valves 710

through 719 on/off

Elevator position #1 through 4

Lid interlock on/off

Chamber pressure

interlock on/off

An analog I/O device 5 provides analog control signals on its output byconverting digital commands that are provided to it to analog signals bydigital to analog converters. It additionally receives analog signalsback from the cassette load lock plasma reactor 23 and the power loadlock reactor 28.

Table 2 provides a listing of the signals that are converted to eitheranalog signals from digital commands provided to the analog I/O device 5by the microprocessor 17 or analog signals received by the analog I/Odevice and converted to digital signals by the D to A's that arecontained within the analog device 5.

Table II Analog commands and inputs for the analog device 5

Inputs analog to digital converters:

1. Manometers 752 and 770 for cassette load lock, 752, 772 and 775 forpower load lock for monitoring pressure.

2. Mass flow control devices 721 through 724 for cassette load lockplasma reactors and 721 through 730 for power load lock reactors

3. RF power control

4. Endpoint detection 50,52

5. Temperature

Commands digital to analog converters

1. Pump rate (throttle valves 704, 706 and 708) for maintaining pressure

2. Flow rate set mass flow valves 721 through 724 for the cassette loadlock plasma reactor and 721 through 730 for the powered load lockreactor

3. RF power set

4. Endpoint detection automatic gain control 50, 52

5. Temperature

It should be noted that the analog I/O is just a parallel combination ofdigital to analog converters or analog to digital converters that areconnected to the data bus 6 and the digital I/O 3 is a plurality of linedrivers and receivers. Control is provided by the analog controller 7which is a microprocessor such as a Texas Instruments 9900 that isprogrammed according to the microcodes that are contained within table3. Any microprocessor that is capable of meeting similar specificationsmay be used however, in lieu of the Texas Instruments 9900.

The data terminal is controlled by data terminal controller 9 whichinterfaces the display 27 and the keyboard 25 to the microprocessor 17as well as displaying the voltage representation that is provided fromthe RF generator 51 and the analog control unit 7 by a data line 12.Table 4 provides the microcode for the data terminal controller 9. Themovement of the semiconductor wafers from each cassette into the reactorchambers and from the reactor chambers into the exit chamber iscontrolled by a slice handler 11 through the operation of stepper motors2 and responding to sensors 4. The slice handler 11 is a microprocessorwhich provides digital commands on its output and receives digitalinputs from the sensors. The microprocessor is a device, again, such asthe TI9900 and the microcode for which is provided in Table 5A is usedby the cassette load lock reactor 23 and Table 5B is used by the slicehandler, in the power load lock reactor 523. The program that is used tocontrol the central processor unit 17 is a complex program and in theembodiment of FIG. 3 has a pascal compiler. A pascal listing of theprograms that are stored within the CPU 17 is provided in Table 6 forthe powered load lock reactor of FIG. 26 and Table 7 for the cassetteload lock reactor of FIG. 2. Tables 3-8 are provided in U.S. patentapplication TI-10892. Table 8 is an assembly language for subroutinesused by the CPU 17 and stored in EPROM 19. TI-10892 is incorporatedherein by reference.

FIG. 4 to which reference should now be made, there is shown a blockdiagram of the control circuit that is used to control the radiofrequency energy that is applied to the load lock reactors 23 and 523.As was indicated in conjunction with FIGS. 1 and 3, the microprocessor17 provides an output command to the RF generator 51 by a control line32. The RF generator 51 includes an RF interface 26 and a generator 28.This is a commercially available unit as manufactured by Plasma ThermInc. or can be a device such as that manufactured by Ortec Incorporatedof Oak Ridge, Tenn. Status of the operation is provided back to thedigital I/O 3 by a data bus 34. The RF output is applied from the RFgenerator 51 and in particular, the generator section 28 of the RFgenerator 51 to the matching network 53 by a conductor 55. The matchingnetwork includes a Bird Watt meter 22, manufactured by Bird Electronicsof Columbus, Oh., which monitors power that is applied to the upperelectrode 30 that is contained within the main chamber 37 by animpedance matching circuit 53. The output of the Bird Watt meter 22 isapplied by an isolation amplifier to the analog to digital converter ascontained within the analog I/O 5 and to the analog controlmicroprocessor 7. Adjustment of the RF energy that is applied to thecassette load lock reactor 23 and power load lock reactor 523 isprovided by the microprocessor 17 of FIG. 3. A digital to analogconverter that is a part of the analog I/O 5, an isolation amplifier 25in the RF interface 26 will cause the RF generator 51 to adjust itsenergy in response to the analog signal that is applied to it. This ofcourse, provides a feedback loop for the host microprocessor 17 tocontrol the plasma operation according to the prescribed menu that isentered by the keyboard 25.

FIG. 5 is a block diagram of the control system that is used to detectthe endpoint of the operation. In the embodiment shown in FIG. 5, thereare dual channels used in the endpoint detection process. Quartz windows58 and 60 provide and optical opening into the main chamber 37.Adjustable filters 62 and 64 can be selected to ensure that only lighthaving the proper wavelength is applied to the endpoint detector 70.There is, as described earlier, two channels, an A channel and a Bchannel. The A channel has a light detector 54 which is a device such asa photo multiplier or silicon detector. The B channel detector 56 ofcourse is a similar device. Each channel has an automatic gain controlcircuit 50 and 52. The gain of the automatic gain control circuits 50and 52 is controlled by the analog controller 7 and the analog I/O 5. Inparticular, the output of the automatic gain control circuit 50 forchannel A is applied to an analog to digital converter 40 that iscontained within the analog I/O 5 and applied to the analog controller 7where the data is processed and passed on the host microprocessor 17.Adjustment of the automatic gain control circuit 50 is provided byeither the host microprocessor 17 and/or the analog controller 7 byproviding a digital command to a digital to analog converter 42 that iscontained within the analog 5. The digital to analog converter 42provides an analog signal to adjust the gain on the automatic gaincontrol circuit 50. The output of the channel B automatic gain controlcircuit 52 is converted to a digital signal by an analog to digitalconverter 44 that is contained within the analog I/O 5 and is processedby the analog controller 7 for averaging of data to be used by thecentral processor 17. An output to set the automatic gain controlcircuit 52 is provided by a digital command being provided by the analogcontroller 7 whether originated from the analog controller 7 or the CPU17 and is converted to an analog signal by the digital to analogconverter 46 and applied to set the automatic gain control of thechannel B automatic gain control circuit 52. Additionally, the displayat 27a provides display of the setting up of the automatic gain control50 and 52. An auxiliary display is provided from the analog controller 7and a digital to analog converter 48. These provide meter displays ofthe endpoint detector circuit.

The operation of the endpoint detector allows the user through thekeyboard entry 25 to define parameters which can be defined as twoclasses, the detection mode and the detection parameters. The detectionmode parameter is selected by the users to provide the following mode ofoperation. No endpoint mode is when the endpoint detector does notoperate. Either channel A or channel B detector outputs can be monitoredand applied to a strip chart recorder via the display outputs 27a.Channel A endpoint selects a signal from channel A detector to be usedto determine the endpoint. The channel B mode selects the signal to beused as the endpoint detection from channel B. The a-b endpointdetection subtracts the output of B from channel A. In this mode, thesignal used for endpoint detection is formed by subtracting the detectorB signal 56 from that of the A detector 54. The purpose of this mode isto allow the signal to noise ratio of the combined signals to beincreased by removing correlated noise during the subtraction process.The final mode of operation is the a+b mode in which the detectoroutputs from channel B are added to the detector outputs from channel A.This mode is useful to increase the available amount of total signalsfor the detection process. FIG. 6 provides a flow diagram of theadjusting of the automatic gain control circuits 50 and 52 and theoperation of the endpoint detector circuit as is programmed by theanalog controller 7. The endpoint detector of FIG. 5 is designed todetect the endpoint when the following parameters are set. The windowlength, T(w) is the time interval during which endpoint signal aftersignal process must remain greater than its selected threshold value forthe endpoint to be determined. The filter factor T(k) determines thetime interval used to perform the digital differentiation of theendpoint signal by the microprocessor 7. The +/- threshold V(t) is thepercent of voltage of an upper limit, such as eight volts in theembodiment of FIG. 5 and is said to correspond to either positive ornegative slope endpoint signal. This threshold is selected as a percentof the maximum voltage. The delay to detector time T(d) is in units ofseconds as the time interval from the application of RF energy to themain chamber 37 to the start of endpoint detection. For example,entering of a number 40 to the keyboard 25 means that the endpointdetector will not start looking for the endpoint until after 40 secondshas expired after the RF energy is applied to the main chamber 37 by theRF generator 55. FIG. 6 is a flow diagram of the process in which themicroprocessor 7 is used to perform all the signal processing for theendpoint detectors. After the initialization of turning on RF energy atcircle 100, the unit waits for the delay to detect time to expire atdiamond 101. The adjustments of the AGC units 50 and 52 is performed atblock 102 and in the embodiment of FIG. 5, the AGC is adjusted toprovide an output of five volts. The AGC is then sampled and in theembodiment of FIG. 5, the sample rate is every one-tenth second. This isillustrated by the control loop at 103 and includes the steps of readingthe signal level at block 105, converting the signal level to a digitalsignal by the analog digital controller of either 40 or 44 at block 106computing the average signal over a period of time over block 107,computing the difference using the filter factor at block 108 andcomparing to see if the difference or summation i.e., a-b, a+b or eithera or b is greater than or equal the threshold voltage at block 109. Thisloop continues until the difference including at block 109 is greaterthan or equal to the voltage threshold in which case the rendered lengthis incremented to insure that the window length has expired as indicatedin by control loop 110. If the window length has expired, than anendpoint detection is indicated at block 111 and the operation iscomplete and exited from at circle 112. It should be noted that inperformance of the AGC operation, the analog controller 7 reads a dataword, interprets it as a voltage, compares it to a reference such as 5volts. It then computes a gain adjustment word and sends it to thedigital to analog converter either 42 or 46 which converts a digitalword into a voltage level. This voltage is applied to the automatic gaincontrol circuit either channel A AGC 50 or channel B AGC 52, of thecircuit which act as of course a multiplier. In this matter, the gain isadjusting using a successive approximation until the output of either orboth the channel A AGC50 or the channel B AGC52 is at a predeterminedvoltage level which in the embodiment of 55 is five volts.

FIG. 7 illustrates the operation of the control loop of FIG. 6graphically. In particular, FIG. 7a is a curve that illustrates thesignal level output from either the A detector 54 or the B detector 52by waveform 114. In FIG. 7b, waveform 116 illustrates the output fromthe analog controller 7 as is displayed on the auxiliary 1 output of thedisplay 27a in which at point 118 the RF power is turned on. The windowT(w) is represented by dimension lines 115. At point 119, the thresholdvoltage V(t) is exceeded and the endpoint is detected. When an endpointis detected, a square wave output as illustrated by waveform 116 isproduced.

GAS AND VACUUM CONTROL SYSTEM

The vacuum and gas control system for the cassette load lock plasmareactor 23 is illustrated in FIG. 8 to which reference should now bemade. The gas from the gas distribution 43 of FIG. 1 is applied to amanifold 750 by a mass flow controller 721 through 724. The mass flowcontrollers are controlled by the analog inputs from the control system10 and additionally valves 710 through 713 are controlled by the statusI/O 3 of the control system 10 and are on/off valves. The gases mixed inthe manifold 750 and applied to the main chamber 37 where thetemperature of the reaction within the main chamber is monitored by athermocouple 751. The thermocouple 751 is an analog input to the analogI/O 5 of the control system 10. A vacuum pump 31 pulls a vacuum in themain chamber 37 when the block valve 709 is open. The flow rate iscontrolled by a throttle valve 708 which position is fed into the analoginput and is set by the output from the analog input of the controlsystem 10. Sensors 2 senses the position of the silicon wafer within themain chamber 37. The vacuum of the entry load lock 21 and the exit loadlock 49 is provided by pump 29 as was discussed in conjunction with FIG. 1. Gate valves 705 and 707 are set open and the pump rates arecontrolled by throttle valves 704 and 706. The gate valves areinterfaced in the control system 10 at the digital I/O 3 and thethrottle valves 704 and 706 are controlled by the analog I/O card 5.Additionally, the positioning of the semiconductor wafers within theentry load lock 21 and the exit load lock 49 is provided by the sensors2 and motors 4.

FIG. 9 to which reference should now be made is shown the gas and vacuumflow diagram for the power load lock 523. The difference in the poweredload lock 523 and the cassette load lock 23 is due to the fact that theentry load lock can have a plasma reaction as well as the exit load lock49. In this case there are 2 vacuum pumps required. 29a and 29a. Theentry load lock has a gas manifold 760 which mixes three gases fromthree mass flow control valves 725 through 727 which are controlled bythe analog inputs and outputs from the control system 10 and areactivated by setting of gate valves 714, 715, 716. The exit load lock 49can have a plasma reaction based upon the mixture of up to three gasesin a manifold 761 that are controlled by mass control valve 728, 729 and730. The on/off operation of the gas flow into the manifold 761 isprovided by the digital I/O 3 of the control system and controls thevalves 717, 178, 719 as is the case with the gas valves into the entryload lock 21.

In FIG. 10, cassette load lock reactor to which reference should now bemade, there is shown a front view of the cassette load lock reactor 23in which the keyboard 25 provides, as discussed earlier, a data entrypoint that is the information of which is displayed on a display 27. Thedistinguishing features of FIG. 10 also illustrate a quartz windowcovered with plexiglass or other plastic 120 for viewing by the operatorof the plasma reaction that is going on within the main chamber 37. Thisalso enables the operator to insure that the semiconductor wafer is inthe proper position between the electrodes during the reaction process.Additionally, the tuning of the RF generator 51 is illustrated by tuningmeter 123 and the DC voltage that develops across electrodes isdisplayed by the DC voltage meter 122. This of course, in FIG. 3 isprovided by the analog control 7 to the terminal controller 9 via dataline 12.

FIG. 11 is a top view of the cassette lock load plasma reactor 23 inwhich the keyboard 25 is illustrated showing switches 133, and keypads135. The cassette that contains the semiconductor wafers to be processedis placed within the entrance load lock 21 by lifting a vacuum tight lid137 and rotating it around hinges 124 to place the cassette into theentrance chamber 21. Glass window 128 provides for visual inspection ofthe placement and the transfer of the semiconductor wafers from theentrance load lock 21 to the main chamber 39. Similarly, at thecompletion of the process of a cassette of semiconductor wafers, the lid139 of the exit load lock 39 is lifted by rotating the lid 139 aroundthe hinges 126 by removal of a cassette of processed semiconductorwafers.

SEMICONDUCTOR WAFER HANDLING INCLUDING TRANSPORT ARM

FIG. 12, to which reference should now be made, there is shown acassette 141 containing a plurality of semiconductor wafers or slices143. A slice transport arm 145 is placed into the cassette 141 and thecassette 141 is lowered by an elevator 156 that includes lead screw 152,stepping motor 4, and sensor 2, until the semiconductor wafers 143 reston the slice transport arm 145 in the middle of the slice opening 147.Because the slice is not touching any part of the cassette as it leavesduring the rotation of the slice transport arm, there is no frictionbetween the semiconductor wafer 143 and the slice handling arm 145. Thisfeature minimizes particular generation as the slice leaves the cassette141. The position of the slice transport arm 145, the cassette 141 arecontrolled by the slice handler 11 of FIG. 3 and the motors 4 andsensors 2. The cassette platform 154 provides a reference position forthe cassette 141 and thus the exit position of the cassette can bedetermined with the sensor 2 and precise control of the elevator 156.After the semiconductor wafers leaves the input cassette 141, it may beplaced over a primary staging platform 149 or on the reactor substrateas is illustrated in FIG. 13. The semiconductor wafer 143 is lowered tothe staging platform 149 by a lifting assemblies 151 which provide aplurality of lift pins 153 that lifts the semiconductor wafer 143 off ofthe slice transport arm 145. The unloaded arm is then removed from underthe semiconductor wafer 143. When the unloaded slice transfer arm 145 isclear, the semiconductor wafer 143 is lowered onto the staging platform149 which centers the semiconductor wafer 143 through the action of thecentering pins 155. When the entrance slice handling arm 145 is movedunder the platform 149 and the slice after being raised by the pinassembly 151 and the pins 153 are retracted the semiconductor wafer islowered onto the slice transport arm 145. When the main chamber 37 isready to accept a semiconductor wafer 143, the entrance load lock slicetransport arm 145 moves into the main process chamber 37 through thegate valve 35. (FIG. 2) The semiconductor wafer 143 is then lifted offthe slice transport arm 145 and the slice transport arm is then removedfrom the main process chamber. The semiconductor 143 is then loweredonto the substrate within the main process chamber for processing Thesemiconductor wafer 143 is removed from the main process chamber to theoutput chamber 49 by reversing the above discussed sequences and usingthe output chamber slice transport arm 147. FIGS. 14 through 17illustrates the slice transport arm 145 as is used on the entrancechamber transport arm 41 or the exit chamber transport arm 57. A fork151 is designed with touch pads 155 for balancing of the semiconductorwafers 143 thereon. The fork is rotatable around axis 157 which isadjustable through the setting of set screws 159. A main arm 161 rotatesaround axis 163 and is driven by a stepping motor to FIG. 17 which iscoupled to the slice transport arm 145 via coupling means 165 and FIG.15 feed through 180 which is a vacuum tight seal load lock walls 181.The wafer transport arms is mounted to the chamber by mounting bracket164 and through holes 165 and 167. The arm assembly 161 contains a sealchain drive mechanism which is driven by a chain 172 of FIG. 16 whichrotates causing sprocket 175 to rotate the fork 151 after being drivenby sprocket 176 which is connected to the drive shaft 163 and coupling165 of FIG. 15. As illustrated in FIG. 15, the slice transport arm isvery narrow to facilitate it sliding under the semiconductor wafers 143and entering the gate port between the load locks and reaction chamber.

GATE VALVES

FIG. 18 is a side-view showing the entrance or the exit into the mainchamber 37. A gate port 184 allows the slice transport arms 145 totransfer semiconductor wafers 143 into and out of the reactor chamber37. A gate valve 35 or 61 which are identical device is shown in FIGS.19 and 20 and include a gate plate 183 which presses against the sides182 of the main chamber 37 to provide a seal thereto. It is important tokeep particulate emissions at a minimal and this is achieved through acamming action on gate valves. Guide rails 180 and 181 guide the gatevalve 35 or 61 up to the gate plate 183 and comes in contact with stops187 and 186. At this point, the camming action that is precipitated bythe linkage 190 that includes a first arm 191 and second arm 193 goinginto place and locking as shown in FIG. 20 pressing the gate plate 183against the gate stop 186 and 187 and transferring the gate carrier 189into the up position. A spring bias provided by spring 195 holds thegate carrier 189 in the position shown in FIG. 19 until the biasprovided by the spring 195 is overcome by the camming action through therotation of the arms 191 and 193 via the rotation of a drive shaft 197that is controlled by an air cylinder.

FIGS. 19 and 20 to which reference should now be made, illustrates apower load lock plasma reactor unit 522 in which a cassette 400 hundredcontains a plurality of slices and is housed outside of the entry loadlock 21. A process menu is entered into the microprocessor that iscontained within the power load lock plasma reactor 523 and the processsequence begins. A single slice that is housed within the entry cassette400 is moved from the entrance cassette 400 through the isolation gates435 which are devices such as that disclosed in conjunction with FIGS.19 and 20 and is carried to the power entry load lock with articulatedarm 441. The power load lock 21 is pumped down to menanomitor to themicroprocessor through a throttle pressure controller and the pre-etchprocess is begun within the entry load lock 21. The first semiconductorwafer is at the completion of the pre-etch process is moved from theentry load lock 21 through a main chamber bott electrode for etching.This is accomplished in the same manner as was discussed in conjunctionwith FIGS. 1-18. Feedback of the slice movement is accomplished bycapacitive sensors in the load lock chambers and main chamber. Afte thesemiconductor is sensed to be safe in the main chamber and thearticulated arm is sensed to have been moved back from the main chamberinto the entry load lock 21, the isolation are closed and theappropriate gases up to 4 are provided from the gas distribution 45. Itshould be noted that the gas distribution also provides gas to the entryload lock 21 up to 3 for the pre-etch reaction and to the exit load lock37, additionally up to 3 gases may be applied there for post-etching andof course all of these are in addition to the purge gas which in theembodiments of these are in addition to the purge gas which isembodiments of FIGS. 1, 19 and 20 is nitrogen. As prescribed by the menuthat has been entered by the keyboard 25, pressure stabilized by athrottle valve capacitor menanomitor feedback to the microprocessor, RFpowr is activated and applied from the RF generator 51 and automaticallytuned by the RF matching network as was discussed in conjunction withFIG. 4, with control feedback from the reflected power to themicroprocessor 7. Etching of the film is automatically terminated by themicroprocessor 7 via the feedback from the endpoint detector as wasdiscussed in conjunction with FIG. 6, seeing a major change in theoptical emission at a given wavelength. Of course, multiple menus can berun on the same slice by the proper selection during menu entry.

At the completion of the process, the semiconductor wafer isautomatically removed from the main chamber 37 by an articulated arm 57in the exit load lock 59 and placed in the exit load lock for thepost-etching process. After processing in the post-etching load lock,the semiconductor wafer is moved to the exit elevator cassette 401 byarticulated arm 541. Additionally, cooling is provided to the mainchamber as well as the post-chamber and the entry chamber viatemperature controller 63. Viewing windows 461, 462 allows viewing ofthe post-etch and pre-etch operation respectively. FIGS. 21 and 22 aremechanical illustrations of the articulated arm 441 and 541 in whicheach has a fork 555. The articulated arms are mounted to the power loadlock assembly by pedestal 453 and include a central arm section 161which rotates around azis 163 as was discussed in conjunction with FIGS.11, 12, and 13.

ELECTRODE AND COLLIMATOR

FIG. 21 is a sectional view of the main chamber 37 as seen from sectionlines 23 of FIG. 19. Initial input of the semiconductor wafer 143through the opening 145 onto a substrate or wafer plate 206. The waferplate is in position to allow clearance for the semiconductor wafer 143and the fork 151 to position the semiconductor wafer over the waferplate 206. Pins 153 will lift the semiconductor wafer off of the fork151 and after its removal, lower the semiconductor wafer onto thesubstrate or wafer plate 206. The embodiment shown in FIG. 26 provides atwo position substrate. It is generally accepted that during processingin the powered load lock that the substrate should be at differentpositions for different modes of operation, such as 0.040 inch for oxideprocessing. In the case of the cassette load lock, the substrateposition is varied only for oxide processing, in all other etching modesthe substrate is stationary. To achieve this, the wafer plate 206 hastwo positions, a low position, which is expanded and a process position.

In the embodiment of FIG. 25, two stainless steel bellows aninterbellows 220 and an outer bellows 221 form a chamber between thebellows at 224. By introducing compressed air into lines 211, pressureis built up in the chamber between the bellows and this causes themovement of the substrate 206 to be implemented. Under initialoperation, air is introduced into, an air cylinder, not shown, whichraises the pins 153 for removal of the semiconductor wafer 153 from thefork 151. The centering pins 155 are raised by introducing air into aircylinder, not shown, which brings the guides 155 into position to centerthe semiconductor wafer 143 onto the wafer plate 206. The wafer plate206 is in position for the process which is defined by the opening asindicated by dimension lines 228 between the cathode 230 and thesubstrate or top of the wafer plate 206. A consistent process gapbetween the cathode 230 and the substrate 206 is maintained duringprocessing. A consistent opening for movement of the semiconductor wafer143 between the collimater 430 and the substrates 206 is also maintainedduring slice movement. A constant low pressure (1 TORR) is maintained inthe main chamber 37 during slice handling, this eliminates the slicecontamination caused by lifting of the main chamber to the atmosphericpressure and facilitates the use of the slice transport arm 141.

Line 212 FIG. 21 is connected to the gas distribution 43 via filters 45(FIG. 1) and provides for the entrance of gas to be processed in betweenthe cathode 230 and the substrate 206. Lines 210 allow for cooling ofthe process reaction by the temperature controller 63 to flow throughchannels 232 and 242 to cool the semiconductor wafer 143 when placed onthe wafer plate 206. Ring 205 is an isolation substrate ring that isisolated from the substrate 206 via isolation assembly 207. The ringconsists of the body of the ring itself, 205, a retractible slicecentering lip 209, isolation mechanism 207 which is made of a metal butwith small thermal contact or with an insulator such as teflon whichmore completely isolates the ring 205 thermally and electrically with apossible ring extension shown at 231. The ring extension 231 is ofcourse to increase the surface area of the top of the ring whichincreases the area of the overlap between the ring and the collimatoritself in the electrode assembly 240.

This extension has been found to improve the effectiveness of thecollimator in eliminating plasma expansion beyond the outside ring. Thering 205 is used to provide isolation and to aid in the control ofplasma discharge which occurs during the reactor process between thecathode 230 and the substrate 206. The electrode assembly includes anelectrode or cathode 230 to which RF voltage is applied via attachmentto the plate 250. The electrode or cathode 230 is surrounded by acollimator 430, which includes insulator 251, which is in turnsurrounded by a grounded plate 252 to all of which have a cylindricalsymmetry about an axis position through the center of the electrode asindicated by line 256. When placed a small distance above a flatgrounded substrate 206, the electrode assembly creates a volume asindicated by dimension lines 228 which can effectively confine a highpower density plasma, while maintaining a sufficient channel for flowinggas through the lines 212 in the direction as indicated by arrows 258and for observing the plasma optically through the window 120. Asdiscussed earlier, the chamber can be widened for automatic transport ofthe semiconductor wafers from outside of the main chamber 137. By havinga confined high power density plasma, high rate uniform anisotropicetching, especially for silicon dioxide and silicon nitrides, can beachieved. The ring 208 has an annulus of a width equal to the distancebetween the placement pins 155 and pin 209 and is an area which isgenerally exposed to plasma due to the fact that most semiconductorwafers have a flat portion that is used for alignment. The reactingplasma will attack the semiconductor wafer plate 206 or substrate andcreate damages. In FIG. 22, by anodizing an area 208 around thesubstrate 206, an area in width as indicated by dimension lines 270 willprevent etching of the substrate 206 when as shown in FIG. 21, asemiconductor wafer 143 is placed on the substrate 206. In general, thesubstrate 206 is manufactured with aluminum which is highly corrosive ifnot protected by anodization.

The cathode assembly 230 of FIG. 21 is shown in FIGS. 24 and 24 andinclude a top plate 269 and a bottom plate 268. The top plate 269 has agas inlet 305 to allow the cooling gas to enter via from line 212 and awater cooled line 304 which removes heat from the plate 268. Recess gasflow channels are provided at 307 and areas 306 provide for thermalcontact between the bottom plate 269 and the top plate 268. The bottomplate 269 is illustrated in FIG. 23 and the top plate 268 is illustratedin FIG. 24. The thermal contact area must be maximized withoutrestricting the gas flow. This is illustrated in the top plate wherethere are many drilled holes in area 301 and the lines in 302 allow forgas flow channels for the top plate 268.

FIG. 25 is alternate embodiment of the substrate 206 which has dualpositions. The alignment pins 155 and lift off pins 153 are controlledby lifting of the carriage assembly 312 which is guided into place bywheels 310. The carriage assembly 312 is lifted by the levers 311 beingraised under compressed air applied to a cylinder contained within ahousing at 313. The positioning of the substrate 206 is accomplished byfeeding air in between an interbellows 220 and an outer bellows 220 intoa chamber 212 at air ducts 211 which causes the wafer plate 206 to beraised or contracted depending upon the air pressure that is containedwithin the air chamber 224.

INSERT E--POWERED LOAD LOCK REACTION

FIGS. 31 through 34 illustrate the load lock chambers which provide forpre-etch processing in the entrance load lock through a plasma assistedreaction, and post-etch processing in the exit load lock through aplasma assisted reaction. In FIGS. 31 and 32 the gas from the gasdistribution manifold 760 is applied by line 781 through a baffling port999. The feedthrough 886 as shown in FIG. 32 provides for movement oftubing 781 to provide for adjustable spacing of the electrode assembly987 to control the volume of reactants area 988. This is illustrated inFIG. 32. In addition to the tubing 786, the electrode assembly 987includes feedthrough 886 and O ring seals 981 and includes a gasdistribution assembly 889, a retainer 888 that holds the electrode 890onto the gas distribution assembly 889. The retainer 888 also seals theelectrode assembly 987 to the walls of the collimator 891, which is madeof insulating materials. The gas is distributed through the electrode890 by means of plurality of distribution holes 991. The slice handlingmechanism which is shown at 882 has a fork 873 which lifts a slice fromoutside of the load lock chamber and centers it on ring 876 and thenrotates around axis 877 to position the slice over the bottom electrode875. The spacing 871 and 872 is 1/8 of an inch so as to minimize itseffect on the plasma that is contained within volume 988. The slicehandler 441 was discussed in conjunction with FIGS. 29 and 31. Thesubstrate 875 has cooling channels 879 to facilitate the cooling of itssemiconductor slice that is mounted to the substrate during itsreaction. Function 870 is designed and positioned so as to ensure thatthe gaps 871 and 872 are at a minimum.

FIG. 34 illustrates the bottom electrode in which the reactant gases areremoved from via line 896 which goes to vacuum pumps 29a or 29b andincludes a mechanical housing 885 and a bellows chamber 884. Within thebellows chamber 884 is a bellows assembly 878 which moves the bottomsubstrate 875 by the operation of an air cylinder pressing shaft 978 inthe upper or lower position. The compressing of the bellows 878positions the substrate 875 to ensure the proper reaction as wasdiscussed in conjunction with the main chamber.

Although the embodiments of the invention have been described with someparticularity, one skilled in the art would know that the substitutionof elements will not depart from the scope of the invention as limitedto the appended claims.

We claim:
 1. A substrate ring assembly for use with a substrate, whereinthe substrate is for supporting a semiconductor wafer and for serving asan electrode for a plasma discharge to process the supportedsemiconductor wafer, comprising:a floating electrically conductingsubstrate ring circling the substrate; and a conductive electricallygrounded collimator which rings and is insulated from the firstelectrode to contain the plasma within a space defined by substratering, substrate, collimator and first electrode.
 2. The substrate ringassembly of claim 1 wherein the substrate ring is thermally isolatedfrom the substrate by means of a thermal isolation assembly disposedbetween the substrate ring and the substrate.
 3. The substrate ringassembly of claim 1 wherein the first electrode is an RF powered cathodeand the substrate is electrically grounded.
 4. A plasma reactiondischarge assembly for confining a plasma reaction to a restricted spacein which a semiconductor wafer may be plasma processed, comprising:afirst electrode; a substrate opposing the first electrode, wherein thesubstrate is for supporting a wafer and generating a plasma dischargebetween the first electrode and the substrate; an electricallyconductive substrate ring disposed around the periphery of thesubstrate, wherein the substrate ring is for aiding in confining aplasma reaction to the restricted space; and an electrical isolationassembly for electrically isolating the substrate ring from thesubstrate; and a solid electrically grounded electrical conductordisposed about the periphery of, and insulated from, the first electrodefor aiding in confining the plasma reaction to the restricted space,wherein the restricted space is the space defined by the groundedelectrical conductor, the first electrode, the substrate, and thesubstrate ring.
 5. The plasma reaction discharge assembly of claim 4wherein the grounded electrical conductor is opposite the substratering.
 6. The plasma reaction discharge assembly of claim 5 wherein thesubstrate ring, the grounded electrical conductor, and the firstelectrode are cylindrically symmetrical about an axis through the centerof the first electrode.
 7. The plasma reaction discharge assembly ofclaim 6 wherein the first electrode is an RF powered cathode.
 8. Avacuum chamber assembly for plasma processing semiconductor wafers,comprising:a vacuum chamber containing: an electrically conductivesubstrate for supporting a semiconductor wafer and for serving as afirst electrode for a plasma discharge; and an electrically conductivesubstrate ring encircling the substrate to aid in confining the plasmadischarge within a space circumscribed by the substrate ring; and asecond electrode opposing the substrate; an electrically groundedcollimator ring encircles and is electrically isolated from the secondelectrode, and cooperates with the substrate ring to aid in confiningthe plasma discharge.
 9. The vacuum chamber assembly of claim 8 whereinthe substrate ring is electrically isolated from the substrate.
 10. Thevacuum chamber assembly of claim 9 wherein the collimator ring opposesthe substrate ring and forms a gap between the collimator ring and thesubstrate ring, wherein the gap will not support a plasma.
 11. Thevacuum chamber assembly of claim 9 wherein the second electrode is an RFcathode.